Saturday, August 22, 2015

As California Goes, So Goes the Country: Welcome to Our Hotter Future

A firefighter battles the "Cabin Fire" in the Angeles National Forest near Los Angeles, Calif. (Credit: Reuters/Jonathan Alcorn) Click to Enlarge.
On the U.S. Drought Monitor’s current map, a large purple bruise spreads across the core of California, covering almost half the state.  Purple indicates “exceptional drought,” the direst category, the one that tops both “severe” and “extreme.”  If you combine all three, 95 percent of the state is covered.  In other words, California is hurting.

Admittedly, conditions are better than at this time last year when 100 percent of the state was at least “severe.”  Recent summer rains have somewhat dulled the edge of the drought, now in its fourth year.  Full recovery, however, would require about a foot of rain statewide between now and January, a veritable deluge for places like Fresno, which in good times only get that much rain in a full year.

To be clear, the current drought may not have been caused by climate change.  After all, California has a long history of periodic fierce droughts that arise from entirely natural causes, some of them lasting a decade or more.  Even so, at a minimum climate change remains a potent factor in the present disaster.  The fundamental difference between California’s current desiccation and its historical antecedents is that present conditions are hotter thanks to climate change, and hotter means drier since evaporation increases with temperature.  Moreover, the relationship between the two is non-linear:  as temperature creeps up, evaporation gallops. Bottom line:  the droughts of the future will be much more brutal — and destructive — than those of the past.

California is already on average about 1.7 degrees Fahrenheit hotter than a century ago, and its rate of warming is expected to triple in the century ahead.  The evaporative response to this increase will powerfully amplify future droughts in unprecedented ways, no matter their causes.

Throughout the state, draconian cutbacks in water use remain in force.  Some agricultural districts are receiving 0 percent of the federally controlled irrigation water they received in past years, while state water deliveries are running at about 15 percent of normal.

Meanwhile, a staggering 5,200 wildfires have burned in the state’s forests and chaparral country this year, although timely rains everywhere but in the northern parts of California and the rapid responses of a beefed-up army of firefighters limited the burning to less acreage than last year — at least until recently.  The blow-up of the Rocky Fire, north of San Francisco, in the early days of August — it burned through 20,000 acres in just a few hours — may change that mildly promising statistic.  And the fire season still has months to go.

So how is this a trendsetter, a harbinger for lands to the east?  California’s drought is deep and long — we don’t yet know how long — and the very long-term forecast for an immense portion of western North America, stretching from California to Texas and north to South Dakota, is for a future of the same, only worse.  Here is the unvarnished version of that future (on which an impressive number of climate models appear to agree) as expressed in a paper that appeared in Science Advances last February:  “The mean state of drought in the late 21st century over the Central Plains and Southwest will likely exceed even the most severe mega-drought periods of the Medieval era in both high and moderate emissions scenarios, representing an unprecedented fundamental shift with respect to the last millennium.”

Let’s unpack that a little bit:  principal author Benjamin Cook of NASA and his colleagues from Columbia and Cornell universities are saying that climate change will bring to the continent a “new normal” more brutally dry than even the multiple-decades-long droughts that caused the Native American societies of Chaco Canyon and Mesa Verde to collapse.  This, they add, is now expected to happen even if greenhouse gas emissions are significantly lowered in the decades to come.  The impact of such droughts, they conclude, will exceed the bounds of anything known in the history of the continent or in its scientifically reconstructed pre-history.

In other words, the California drought of recent years offers only a foretaste of what is to come. Incidentally, Cook, et al. are by no means outliers in the literature of climate prediction.  Other important studies with similar forecasts support a steadily broadening consensus on the subject. 

And North American droughts will have to compete for attention with countless other climate change impacts, especially the hundreds of millions of refugees worldwide who will be put into motion by rising sea levels and other forces that will render their present homes unlivable.

Read more at As California Goes, So Goes the Country:  Welcome to Our Hotter Future

No comments:

Post a Comment